Geothlypis formosa

Phylogenetic analyses of sequences of mitochondrial and nuclear DNA (Escalante et al. 2009, Lovette et al. 2010) indicate that several species often placed in Oporornis (tolmiei, philadelphia, and formosa) are more closely related to Geothlypis species than to Oporornis sensu stricto (cf. Lowery and Monroe 1968).

Large breeding range in the eastern (mainly southeastern) U.S. but declining in recent decades, due most likely to loss and fragmentation of breeding and/or winter habitat.

BREEDING: from southeastern Nebraska, east across central Iowa, southwestern Wisconsin, northeastern Illinois, central Indiana, north-central Ohio, southern Pennsylvania, northern New Jersey, and southeastern New York, to southwestern Connecticut, south to Texas, Gulf Coast to northwestern Florida, central Georgia, and South Carolina, and west to eastern Kansas and central Oklahoma (AOU 1983). NON-BREEDING: tropical zones of southern Veracruz and Oaxaca, through Chiapas, the base of the Yucatan Peninsula, primarily on the Caribbean slope of northern Central America, throughout Costa Rica and Panama, and into northern Colombia and northwestern Venezuela (AOU 1983, McDonald 1998). Uncommon transient through the West Indies; some may overwinter on eastern and southern West Indies islands (McDonald 1998). Birdlife International (2014) estimates the range size to be 1.1 million square kilometers.

This species has an extremely large range and population size (Birdlife International, 2014) so it should meet the lower limits of the EO range.

Probably adversely affected by forest fragmentation. Whitcomb et al. (1981) reported that populations were only 33% of their maximum potential in forests less than 173 acres (70 ha). Nesting was reported in higher densities at distances approaching 200 ft (61 m) from transmission-line corridors (Kroodsma 1982, Chasko and Gates 1982). Pairing success and territory density were examined in populations occupying small (< 140 ha), isolated forest fragments in an agricultural setting and larger (> 500 ha), contiguous forest tracts in central Missouri by Gibbs and Faaborg (1990). Densities did not differ between fragmented (2.1 males per 10 ha) and contiguous sites (1.9 males per 10 ha), and the proportion of paired and unpaired males was identical between the two forest types. Gibbs and Faaborg (1990) suggested two reasons for the lack of sensitivity to forest area. First, the fact that breeding occurs in heavily vegetated creek-bottoms where nests are inconspicuous may alleviate predation pressure. Second, food (herb and shrub invertebrates) is unlikely to be affected by the increased local evaporation rates and decreased soil and litter moisture levels associated with forest area reduction. Loss of tropical forests may also contribute significantly to the regional declines that have been observed in temperate North America. Some declines parallel deforestation in the tropics, and habitat fragmentation on the breeding grounds cannot account completely for these declines. 1980). According to Bent (1953), a common victim of the brown-headed cowbird (MOLOTHRUS ATER); in parts of Pennsylvania, historical records cite the warbler as the commonest victim of the cowbird. More recently, Robinson (1992) documented brood parasitism by cowbirds, although his data, as well as McDonald's in Virginia, indicate that ground-nesters appear to be less susceptible than shrub-nesting species. Of six nests in central Illinois, two were parasitized with an average 0.8 cowbird eggs per nest and an average 3.0 cowbird eggs per parasitized nest (Robinson 1992). In total, three warblers and one cowbird were raised; in no cases were warblers and cowbirds raised together at the Illinois site. At McDonald's Virginia site, the intensity of cowbird parasitism over 14 years has varied annually from 0% to about 15% of the known nests and fledged families. No correlates have been identified, however, to account for this variation (McDonald, unpubl. data). Unlike the Illinois study, in Virginia warblers and cowbirds were raised and fledged together successfully, with no species-specific survival differences. Predation on nests is probably more common than usually realized because the parents simply start re-nesting within a week unless the nest was destroyed very late in the season (McDonald, unpubl. data). Bent (1953) stated that snakes and other prowling predators have been known to rob nests. At McDonald's site in Virginia, about one-fourth of the nests were depredated before fledging. Indirect evidence, including disturbance of the nest cup, and the results of experiments at the same site on artificial nests, suggest that the major predators at this site are small mammals (e.g., eastern chipmunk [TAMIAS STRIATUS]) and medium-sized mammals (raccoon [PROCYON LOTOR], skunk [MEPHITIS MEPHITIS], and opossum [DIDELPHIS VIRGINIANA]). It is not unlikely that snakes and corvids also prey on these nests (McDonald, unpubl. data). The only documented cases of predation on adults include a bizarre report of one being captured and consumed by a box turtle (TERRAPENE CAROLINA) and McDonald's finding remains of a banded female at her nest of four 7-day-old nestlings, also mostly consumed. A medium-sized mammalian predator, such as a raccoon or opossum, common at the Virginia site, were suspected in the latter predation event.